1. Field of the Invention
The present invention relates to a control device for a mobile robot, such as a legged mobile robot.
2. Description of the Related Art
As a technique for controlling a legged mobile robot, such as a bipedal walking robot, there has been generally known so-called position control proposed in, for example, Japanese Patent Application Laid-Open No. 5-305579 by the applicant of the present application. According to the disclosed technique, the desired displacement amount of each joint of a robot is sequentially determined on the basis of a desired motion of the robot (e.g., the trajectory of a desired position of the distal end of a leg of the robot), and then the actuator of each joint is drivably controlled so as to cause an actual displacement amount to coincide with the desired displacement amount.
According to the position control described above, the actual displacement amount of a joint is maintained to be constant as long as the desired displacement amount of the joint remains constant, thus inconveniently presenting poor flexibility in response to a change in an external force acting on the robot.
As a solution to the inconvenient inflexibility, there has been known a technique disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-160446. According to the technique, a spring member is interposed between a joint and an actuator to impart flexibility to the joint, and a desired driving force for each joint to accomplish a desired motion of a robot is determined by inverse dynamics calculation so as to control the actual driving force of each joint to the desired driving force thereof by so-called force control.
In a mobile robot, such as a bipedal walking robot, if a spring member is provided between a joint and an actuator, as with the technique disclosed in the aforesaid Japanese Patent Application Laid-Open No. 2007-160446, the displacement amount of each joint of the robot tends to change in response to, for example, a change in an external force acting on the robot. This easily causes the overall center-of-gravity point of the robot to fluctuate.
Especially when the position of the overall center-of-gravity point of the robot changes in a vertical direction, the overall center-of-gravity point frequently vibrates in the vertical direction accordingly, possibly leading to a resonant vibration. Such a vibration may make it difficult to stably accomplish a desired motion of the robot.